@Aurélien Gâteau
Mandy’s lines were left starkly black as that is how all characters are drawn on her show. I didn’t want to mellow her out any.

@Jonathan Carter
For the coloring, I do all the work on different transparent layers under the layer with just the lines (as many as I need). I will usually use the paint brush for small areas. For larger areas, I will often use the free select tool to define the area inside of my lines, and then fill. For some of the tighter spots it’s often easier to just paint right through to the outside area and then erase the extra later. Sorry if that’s a horrible explanation. I did a video here http://www.youtube.com/watch?v=SiyiiaaHtPw

There’s another way you can cheat if you have really thick lines. Make a transparent layer then fill it with a solid color (We’ll call this our palette). Then on the layer with your lines, use the select by color so the current “selection” is all the lines of your drawing. Now go back to the “palette” layer and we’ll shrink that selection down just a bit by using select -> shrink by 2-3 pixels. Last step on this palette layer is to cut that selection. You will essentially be left with a bunch of solid color shapes that are not connected, which you can simple us the bucket tool on to fill. This is essentially how I color in Inkscape as well. (TIP: If the most prevalent color is the one you choose to initially fill your “palette” with, that will save you some time.)